Because of the many analogies between oncogenesis and embryogenesis, we made preliminary studies of the distribution of 67Ga in pregnant animals. These studies showed marked concentration of the isotope in placental and mammary tissues and concomitant lack of uptake in thymus. Tumor-bearing rats also show diminished 67Ga uptake in thymus tissues. We propose to study the tissue distribution of 67Ga at various stages of embryogenesis in the rat and rabbit. The study of 67Ga distribution in pseudopregnant or hormonally treated, ovariectomized animals will determine the degree to which the alterations of 67Ga distribution in pregnant animals is related to hormone action in the absence of fetal tissue. We plan to isolate the subcellular and molecular species that bind 67Ga in fetal and maternal tissues at various stages of gestation. Antisera prepared against the 67Ga binding fractions isolated from rat placenta will be tested for cross reactivity with 67Ga binding fractions extracted from rat tumors and from normal thymus tissue. We will study the association of 67Ga localization with fetal antigen expression in the hamster in vivo and with human carcinoembryonic antigen in vitro. The relationship between activation of RNA-directed DNA polymerases and 67Ga binding in endometrial tissue will also be studied. Should 67Ga binding by tumor tissue be related to specific fetal protein expression, the clinical usefulness of 67Ga could be increased in that localization or lack thereof would be indicative of the nature of the tumor. Likewise the relationship between gallium-binding moieties in thymus, placental and tumor tissue could provide a new tool to study the host response to both fetal and neoplastic tissue.